Heretofore, a magnetoresistive change element has been used mainly as an element for reading in a magnetic field from media of a hard disk drive. The magnetoresistive element utilizes a magnetoresistive effect of changing electrical resistance by application of a magnetic field to the element, and hard disk drive industry uses a TMR head using a tunnel magneto resistance (TMR) effect of exhibiting a greater rate of resistance change than that of a GMR head using a giant magneto resistance (GMR) effect, which in turn achieves a dramatic improvement in record density. Meanwhile, MRAM (magnetic random access memory) which is an integrated magnetic memory achieved by integrating this TMR technology with a semiconductor element has already started its commercialization. The MRAM includes a TMR element made of a magnetic material, formed on top of a semiconductor device, as distinct from SRAM (static RAM) or DRAM (dynamic RAM) which has hitherto been formed of a semiconductor element alone. Moreover, the MRAM enables a dramatic improvement in power consumption because of its non-volatility, and is thus expected to achieve larger capacity, in mobile communication market.
The MRAM uses, as the TMR element, an element of an in-plane magnetization type in which a direction of magnetization of a free layer and a reference layer spins in a direction perpendicular to a direction of a multilayer film, as disclosed in Non Patent Document 1. The MRAM poses the problem of being incapable of large storage capacity because of its large memory cell for storing data. By recent research and development, however, STT (Spin Transfer Torque)-MRAM using spin injection can be expected to overcome a drawback inherent in the MRAM and hence achieve larger capacity. This technology can change a direction of magnetization of the magnetic material by utilizing magnetic moment produced by spin of electrons, thus enabling miniaturization and also a reduction in a current value required for writing of data. Therefore, the STT-MRAM can operate even with a small-sized element and is thus suitable for higher density. The STT-MRAM uses the element of the in-plane magnetization type as is the case with the MRAM, and an element of a perpendicular magnetization type in which the direction of magnetization of the free layer and the reference layer spins in the same direction as the direction of the multilayer film. A typical multilayer film structure of the perpendicular magnetization type is disclosed in Non Patent Document 2. Further, research and development of materials and structures is stepped up so that magnetization can reverse even with the small-sized element, and there has also been a report on a structure in which an oxide layer is formed on top of the free layer, as disclosed in Non Patent Document 3.
Manufacture of the TMR element not only uses the structures disclosed in Non Patent Documents 1 and 2, but also widely uses a sputtering deposition (hereinafter, also called merely sputtering) method which involves sputtering a target made of a desired deposition material thereby to deposit a film on a facing substrate (see Patent Document 1). Further, there is a need for a crystallization annealing device for improving the rate of resistance change of the element, a substrate cooling device subsequent to annealing, and an oxidation device for forming the oxide layer, as well as a sputtering device. In the future, making full use of these devices for development of high-performance element structures as well as materials is essential in order to achieve practical use of STT-MRAM.